Magnetic detector.



No. 772,878.. v W 'PATENTED 00 18, 19.04. v L. DE FOREST.

MAGNETIC DETECTOR.

- APPLICATION FILED JUNE 20, 1903.

no MODEL. i v zsn'nnms-annn'm 1.

' i Arron/Er.

UNITED STATES Patented October 18, 1904.

PATENT OFFICE.

LEE DE FOREST, or NEW YORK, N. Y.

MAGNETIC DETECTOR.

SPECIFICATION forming part of Letters Patent No. 772,878, dated October 18, 1904.

Application filed June 20, 1903. Serial No. 162,458. (No inodel.)

To all whom/ft may concern:

Be it known that I, LEE DE FoREsT, a citizen of the United States, and a resident of the city, county, and State of New York, have invented certain new and useful Improvements in Magnetic Detectors, of which the following is a specification.

My invention relates to improvements in magnetic detectors for wireless telegraphy,

and comprises the features and parts and combinations thereof hereinafter described, and particularly pointed out in the claims.

Figures 1, 2, 3, 4, and 5 are diagrams, by the use of which the features of my invention may be more readily explained.

In the forms of Hertzian-wave detectors heretofore used, operating on the principle discovered and utilized by Rutherford-that is, the demagnetization of a rod or rods by currents aerially induced it has been customary to pass the high-frequency or aeriallyinduced oscillations through a coil of insulated wire surrounding one or a bundle of magnetizable ironor steel wires. On account of the high frequencies and shght intensities of these demagnetizing-currents their effects upon the iron are limited, as pointed out by Rutherford, chiefly to the skin of the iron wires, and I have also found that their effects are largely limited to those lying outermost in the bundle. The inneriron is shielded from the effect and the signaling instrument is therefore but slightly aflected. Again, in order to subject a suflicient amount of surface 35 therefore, to use as the core a hollow cylinder or barrel, preferably of iron wires, with the wave-winding or demagnetizing-coil either within or without this cylinder, or both. Thesignal-coil which is connected to the telephone or signaling device, and in which momentary local currents are induced by the sudden demagnetization-0f the iron by the Hertzian oscillation, I prefer to place on the outside of theiron cylinder. Such an arrangementI have shown in Fig. 1, where I represents the cylinder of straight iron wires, B the wavewindingor demagnetizing-coil, preferably wound in a single layer or in several parallel strands, and D the signaling-coil, connected with the telephone T or such otherindicating device as may be employed. A is the antenna, and E the earth or capacity connection. H is a bar-magnet rotated at a suitable speed near an end of the solenoid by the motor \I. I have found a cylinder of one-quarter-inch inside diameter, three inches long and made up.

' of a transformer the primary of which is connected to the upright conductor and earth, or

' in any other suitable manner subjected to the influence of theHertzian oscillation. Ihave also found it advantageous to use two layers 'or sets of demagnetizing-coils or wave-windinder, and preferably to connect the two windings or coils in parallel... Such a second winding is shown at b, Fig. l. This form, however, will operate successfully if one coil or wavewinding be connected to the antenna only and the other to the ground only, thus giving a capacity effect at the solenoid. This construction is shown in Fig. 5, in which two coils B and B are shown, one within and one without the core formed by the needles I, one coil being connected with the antenna and the other with the ground, there being, however, no direct connection between the two coils. This figure is otherwise like Fig. 1. By thus avoiding the direct or continuous metallic circuit from antenna to earth I findthe disturbances from'atmospheric strays reduced; but the advantage of the multiple connection shown in LCD Fig. 1, as well asin using two or more strands in each demagnetizing-coil and connecting the same in parallel, is to reduce as far as possible the self-induction of the device and its choking effect to these high-frequency oscillations.

The chief reason 1 have found that the forms of magnetic detectors as heretofore ordinarily used are so much less sensitive than devices of the responder or coherer class is that in order to get a suflicient number of ampereturns, while still subjecting the requisite amount of surface iron to the demagnetizing effect of the Hertzian currents, the demagnetizing-coils are given so great a self-induction that a large part of the available current is choked back.

Figs. 2 and 3 show forms which I have very successfully employed to allow maximum demagnetizing effect of the wave combined with minimum self-induction. In the form shown in Fig. 2 I employ a plurality of bundles of fine iron wire 1, each surrounded by its respective demagnetiZing-coil B, in a single layer, preferably of two strands. The several de magnetizing-coils B are preferably all connected in parallel at their ends and placed in the aerial or oscillating-current circuit. Around the mass of bundles is wound the sig naling-coil D, connected to the telephone or other signaling device T, thus bundling them or binding them into a larger bundle. The bundles may be subjected to a varying or reversing magnetic field in one of many ways, as by rotating a magnet H near one end, after the manner shown in Fig. l and by dotted lines in Fig. 2, or by sending an alternating or pulsating current through a coil C, Which surrounds the detector. G is a suitable source of such magnetizing-current, such as an alternating-current generator or a commutator reversing a direct current. In practice 1 have successfully employed six bundles of No. 28 silk-insulated iron wire, seven wires to a bundle, five inches long, each bundle carrying one hundred turns of No. 30 insulated copper wire in two strands, making twelve distinct wave-windings in all, all connected in parallel at their ends. The telephone-coil D used was of three hundred and fifty turns of No. 30 Wire, and the magnetizing-coil,which preferably underlies the telephone-winding, was of two hundred turns of No. 2st wire. The preferred frequency of the magnetic reversals is approximately eight to twelve per secondtoo low to produce an appreciable noise in the telephone T. All the above dimensions may, however, be varied within wide limits, those given being merely instances of proportions which I have found to work well, and the exact arrangement and proportions of energizing, signaling, and wave windings or demagnetizing-coils and of the iron core or coils may be varied in a great variety of ways which will at once suggest themselves to any one skilled in the art and which will still come within the scope of my invention. I do not. therefore, desire to be limited in this invention to any specific form ordimensions herein described. Such another form of detector embodying the same principles is shown in Fig. 3, wherel have shown by a sectional view a center core l, of iron or steel wires surrounded in turn by a demagnetiZing-coil 1%, a cylinder 1 of iron wires, a second demagnetizing-coil If, a second cylinder 1, of iron, a third demagnetizing-coil B, and a third cylinder l', of iron. The demagnetizing-coils may be all connected in parallel, as before. On the exterior vl place a signaling-coil 1), shown as operating a telephone, and an exciting or remagnetizing coil surrounding the core. I have there shown the magnetizingcoil in two parts C and the telephone-coil as between said parts. This form of detector l have also found very sensitive. inasmuch as all portions of a considerable amount of iron are directly subjected to the demagnetixing effect of the Hertzian wave, while at the same time the self-induction of the wave-circuit is very small.

One object sought in my present invention and which is largely embodied in the construction shown in Fig. 3 is to bury the wave-wilulings or demagnetizingcoils, by which I mean the coils which carry the aerially-induced impulse in the mass of the iron to be demagnetized, bringing the two into intimate association and so locating them that the maximum amount of surface iron is brought into the closest possible relation with the said coils. This result may be obtained in a high degree by burying said demagnetiZing-coils in a mass of linely-diyided iron powder or lilings, which may even have the iron mixed among the several turns of the windings.

The form of detector heretofore described may be combined with a telephone in such a avay as to make a single instrument out of it and at the same time get rid of some of the self-induction or choking ell'eet. I have shown the manner of doing this in Fig. 3, in which K represents by dotted lines a telephone-diaphragm placed adjacent the cores of the detector, said detector itself acting as the telephone-magnet. \Vhen so combined, the signal-coil D is not needed. This arrangement avoids the use of a separate coil and magnet for the telephone and makes the telephone and detector a single compact in-- strument and also avoids considerable inductance and choking effect-s. Such a combination of the two instruments is not limited to the form shown in Fig. 3, but may be done with other forms as well.

I have found that if the antemue at a receiving-station consist of several parallel conductors or groups of conductors separated by a few feet a magnetic detector may be connected to the base of each and that each will register'animpulse but little weaker than if but one be employed. Fig.4 shows an arrangement by which I take advantage of this effect to considerably increase the effect on the signaling device by the additive or combined effect on all the detectors. A A A are three antennae, each led to earth through a detector such as I have herein described. The aerial or antenna circuit may include the demagnetizing-coils of the detectors or the cores, as

desired, this feature of interchangeability having been'pointed out by Rutherford. In Fig. 1 I have shown the antennae as connected with the cores and a common ground for all antennae. Where the other connection is usedthat is, to the demagnetizingcoils one more coil than is shown is required, which should be between the core and the innermost coil shown in said figure. The energizing or magnetizing coils of the three detectors may be connected together either in series'or in parallel to any suitable magnetizing source, an alternating-generator G being shown. The three signaling or telephone coils D D D are shown connected in series and to the telephone T or other indicating instrument, which is thus operated uponby the combined currents induced in the three signaling-coils.

In the form here shown there are three separate energizing or magnetizing coils O C 0 This same arrangement may be carried still further and each individual bundle of iron be surrounded with a distinct magnetizing-coil,

thus allowing smaller current intensities in the fluctuating or magnetizing current; but when instead a revolving magnet is applied near the ends of the aggregation of .bundles each of said bundles will be magnetized to an approximately like degree.

It is evident that various equivalent constructions may be substituted for those shown and described and that other combinations and arrangements of the parts may be made without changing the essential character of the inof magnetizable material and a demagnetizingcoil therefor.

2. A magnetic detector comprising a pluralityof wires arranged as a shell and a demagnetizing-coil therefor.

3. A magnetic detector comprising a shell,

of magnetizable material, and a demagnetizing-coil surrounding the same.

within and without said shell.

5. A magnetic detector comprising a shell composed of parallelwires, and a demagnetizing-coil both within and without said shell.-

16. A magnetic detector comprising a magnetizable shell and a demagnetizing-coil both within and without said shell, one of said coils being adapted for connection with the antenna and the other with the ground.

'7. A magnetic detector comprising a magnetizable shell and a plurality of demagnetizing-coils adapted for connection with the antenna and earth in parallel.

8. A magnetic detector comprising a magnetizable material and a demagnetizing-coil embedded therein.

9. A magnetic detector comprising a magnetizable material, and a plurality of demagnetizable coils embedded therein- 10. A magnetic detector comprising a magnetizable material and a plurality of demagnetizing-coils embedded therein and adapted for connection with the antenna in parallel.

11. A magnetic detector comprising a magnetizable material and a plurality of nested demagnetizing-coils alternating therewith.

'12. A magnetic detector comprising a magadapted for parallel connection with. the an tenna.

netizablematerial and a plurality of nested 16. A magnetic detector comprisinga plurality of demagnetizingcoils bundled together and adapted for parallel connection with the 19. A magnetic detector comprisinga plu- .rality of demagnetizing-coils, magnet1zable cores therefor, a signal-coil and a remagnet1z-- ing-coil both common to all the demagnetizing-coils.

20. A magnetic detector comprising a plurality of demagnetizing -'coils bundled together, cores therefor, and a signal-coil common to all said demagnetizing-coils.

21. A magnetic detector comprising a plurality of demagnetiZing-coils bundled together, cores therefor, a signal-coil common to all said demagnetizingcoils and means for automatically remagnetizing the cores.

22. A magnetic detector comprising a series of magnetizable cores adapted to be bundled together, individual means for demagnetizing said cores by the aerially-received impulsesand a common remagnetizing means for all of said cores.

23. A magnetic detector comprising a series of magnetizable cores adapted to be bundled together, individual means for demagnetizing said cores by the aerially-induced impulses, and automatic means for remagnetizing said cores.

24. A magnetic detector comprising a plurality of magnetizable cores,and independent means for demagnetizing each of said cores.

25. A magnetic detector comprising a plurality of magnetizable cores, means for inde pendently demagnetizing each core, and a common remagnetizing means for all cores.

26. A magnetic detector comprising a plurality of magnetizable cores, means for independently demagnetizingeach core, a signalcoil common to all cores,and means for remagnetizing said cores.

27. The combination with a plurality of separated antennae, a magnetic detector for each antenna, and signal-coils for said detectors connected in series.

28. The combination with a plurality of separated antennae, a pluralit v of magnetic detectors comprising solenoids and having their cores connected each with its res wetive antenna, the coils of said solenoids being connected in series with a source ol variable electromotive force, and signal-cores for said detectors connected in series.

29. A magnetic detector comprising a plurality of demagnetizingcoils and cores in parallel with the same antenna and operative upon the same signaling instrument.

30. The combination of a plurality of groups of demagnetizing coils and cores, an antenna for each group, remagnetiZing-coils and signal-operating coils, one for each group and each being in series with the other coils ol like kind.

ln testimony whereof I have hereunto atlixed my signature, this 17th day of June, 1003, in the presence of two witnesses.

LE l) l 1C F0 R EST.

itnesses:

M. \V. NoLAN, ll. L. hin'NoLns. 

